Recent technical advances have indicated that it is desirable to form metallized microelectronic components and interconnects from copper rather than the more traditional aluminum. Copper metallization structures are preferred to the more conventional aluminum structures because the resistivity of copper is significantly lower than that of aluminum. Consequently copper metal components can be made smaller than aluminum components and will require less energy to pass electricity through them, which leads to better processor performance.
Chemical dry etching of copper can be done by a two step chemical reaction. First, copper is oxidized to form copper oxide. Next, the copper oxide is etched away by reacting with hexafluoroacetylacetone (hfacH) gas to form a volatile product. This two step chemical reaction is described, e.g., by A. Jain, T. T. Kodas, and M. J. Hampden-Smith, in Thin Solid Films Vol. 269, pp 51-56, 1995, which is incorporated herein by reference.
First step: Cu+O2→Cu2O, CuO
Second step:
Cuprous oxide: Cu2O+2hfacH→Cu(hfac)2+Cu+H2O
Cupric oxide: CuO+2hfacH→Cu(hfac)2+H2O
Oxidation of copper is usually done by exposing the copper to oxygen gas or species from an oxygen plasma at elevated temperature, e.g., about 150° C.-300° C. At these temperatures, three-dimensional oxide structures are formed, which are determined by the thermodynamics of the oxidation reaction. The three-dimensional structures cause the copper oxide layer to be non-uniform. The morphology of the etched copper surface is determined by the morphology of the oxide/copper metal interface, which is roughened by the formation of these three-dimensional structures.
It is within this context that embodiments of the present invention arise.